Sounds worrying, is the ignition on when you do this and get a spark?
Swapping the blue/black and blue/green shouldn't cause any problem especially if the sender isn't connected. If the sender is connected, then as i said earlier, the gauge won't work until the tank is empty and the reserve lamp will be on all the time.
As long as black/blue, the +ve feed isn't on the wrong pin. Perhaps you have pinched the wires somehow
I've mailed Leo, lets see what we come up with before you go any further